1. Field of the Invention
The present invention relates to a substrate handling apparatus.
2. Description of the Related Art
Conventionally, in semiconductor device fabrication processes, various types of substrate handling apparatuses which handle for example semiconductor wafers and LCD glass substrates have been used.
For example, in a flat-type or upright-type heat treating apparatus, semiconductor wafers are processed over a wafer boat which is made of quartz. To transfer the semiconductor wafers between the wafer boat and a wafer cassette which is made of a resin, a wafer transferring apparatus has been used. An example of the wafer transferring apparatus is a pushing apparatus which is known as a pusher. The pusher pushes up semiconductor wafers which are stocked in a wafer cassette and transfers them to a wafer boat while supporting them.
As is well known, in semiconductor device fabrication processes which form very small electric circuits over substrates, very fine particles tend to adhere to substrates, resulting in defects of final semiconductor devices, which lead to a decrease of yield. Thus, to prevent such a problem, in the above-described wafer transferring apparatus, a substrate supporting portion which comes in contact with a substrate and supports it is formed by molding a block of resin such as Teflon (trade name) in a predetermined shape. Thus, the adhesion of particles to substrates can be prevented and thereby the yield of the fabrication can be improved.
In a substrate handling apparatus such as a wafer transferring apparatus, optical-type or capacitance-type wafer detecting sensors are sometimes buried in the substrate supporting portion made of the Teflon block so as to detect whether or not semiconductor wafers are present on the substrate supporting portion.
However, substrates such as semiconductor wafers tend to be statically charged. For example, after washing process or the like, while a wafer cassette is being transferred, semiconductor wafers contained therein vibrate and thereby they rub each other. As a result, the semiconductor wafers may be charged at high voltages ranging from 10 kV to 20 kV. Thus, in the above-mentioned substrate handling apparatus, due to such a static electricity, an excessive current flows in the sensors and the like which detect whether or not substrates are present. Consequently, the sensors and the like may be damaged or/and the apparatus may malfunction.
To avoid such a problem, the substrate supporting portion may be formed of an electroconductive material such as a metal. In this case, however, the substrates such as semiconductor wafers make contact to the substrate supporting portion made of a metal. Thus, since they rub each other, particles take place.